Practical design and application of Light Emitting Diodes (LED) type devices for use in Area Lighting and like schemes are limited by thermal energy-management issues. LED device manufacturers have generally been aiming at developing LED devices that provide greater light output without significant increase in size of the device. This accentuates the problem of heat management; the energy efficiency of LEDs is relatively low, such that only a portion of the consumed energy is converted to light, while the bulk of the energy is converted into heat. Therefore, by by producing more light intensive LEDs more thermal energy is produced in the same unit volume of the device.
It is known that LEDs exhibit negative temperature coefficient aspects, i.e. at fixed power input, as the device's operating heat rises, the device's light output decreases. The relationship between LED decrease in light output due to increased operation temperature can be expressed approximately as a negative linear relationship between the percentage light output and degree C. increase in temperature. That is, as the LED device's operating temperature increases one ° C. it can by approximated that the device will lose about one percent of its light output.
Attempts have been made in the prior art to solve the negative temperature coefficient issues. As an example, in LED highway traffic signal devices housings with ventilation configurations, both of passive (convection-type) and active (fan-driven-type) have been provided to prevent the LED-s from overheating. Present art LED traffic signal devices also address the inherent negative temperature coefficient nature via the electrical power supply. These approaches either increase power to the device to compensate for light output loss or address the form of the provided electrical power such as sine vs. square wave in an attempt to moderate the production of by-product heat, i.e. waste heat.
There is a long-felt need for LED devices of long service life and high electric power-to-light efficiency.
Solid state thermoelectric modules (TEM) also referred to as thermoelectric coolers (TEC) or heat pumps have been used in various applications since the introduction of semiconductor thermocouple materials. Such devices convert electrical energy into a temperature gradient, known as the “Peltier” effect or convert thermal energy from a temperature gradient into electrical energy. By applying a current through a TEM a temperature gradient is created and heat is transferred from one side, the “cold” side of the TEM to the other side, the “hot” side.
TEMs have been considered unsuitable in the art for cooling LED lighting devices as they have been ruled out for insufficient efficiency; that is, if configured and operated with conventional settings the energy cost of operating a TEM for cooling an LED device is more than the energy gained in operating the LED at a reduced temperature.